The A-12 reconnaissance aircraft was built by Lockheed and tested in 1962. Photo: CIA.gov

The A-12 reconnaissance aircraft was built by Lockheed and tested...

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The only A-12 built, the "Titanium Goose," is shown about to refuel. Photo: CIA.gov

The only A-12 built, the "Titanium Goose," is shown about to...

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A rare photo of an airborne A-12 with its landing gear visible. Photo: CIA.gov

A rare photo of an airborne A-12 with its landing gear visible....

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For testing, the finished A-12 was disassembled and hauled in boxes to Nevada from California, posing some traffic problems. Once, an oncoming bus grazed a crate. Photo: CIA.gov

For testing, the finished A-12 was disassembled and hauled in boxes...

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** FILE ** This is a 1988 file photo of a U-2 spy plane as it takes off from Beale Air Force Base near Marysville, Calif. A U.S. military spy plane crashed in South Korea on Sunday, January 26, 2003, but the American pilot ejected safely, the South Korean Defense Ministry said. Media reports said three people on the ground were injured when the aircraft exploded.

Photo: DAVE NIELSEN, AP

** FILE ** This is a 1988 file photo of a U-2 spy plane as it takes...

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** FILE ** This is an undated file photo released by the Pentagon in 1992 showing a U-2 reconnaissance plane. A new corps of inspectors will soon deploy the U-2 plane in Iraq again, now that the United Nations and Baghdad have broken an impasse that kept the reconnaissance plane grounded. That breakthrough, announced Monday, Feb. 10, 2003, could help set the tone of U.N. debate over pursuing inspections--or preparing for war--in Iraq.

Photo: AP

** FILE ** This is an undated file photo released by the Pentagon...

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This undated photo released by the US Air Force shows a U-2 spy plane similar to the plane that crashed in southwest Asia Wednesday June 22, 2005. The U-2 provides continuous day or night, high-altitude, all-weather, stand-off surveillance of an area in direct support of U.S. and allied ground and air forces. The U-2 is a single-seat, single-engine, high-altitude, reconnaissance aircraft. Long, wide, straight wings give the U-2 glider-like characteristics. The cause of the crash and the pilot's status were not known, U.S. Central Command in Baghdad said in a brief written statement. The crash happened Tuesday night. The military did not immediately provide further details.

Photo: AP

This undated photo released by the US Air Force shows a U-2 spy...

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In an Aug. 4, 1955 photo provided by the CIA, the prototype U-2 spy plane is tested at what became known at Area 51 in Nevada. The CIA is acknowledging in the clearest terms yet the existence of Area 51, the top-secret Cold War test site that has been the subject of conspiracy theories for decades. (AP Photo/CIA)

Photo: Associated Press

In an Aug. 4, 1955 photo provided by the CIA, the prototype U-2 spy...

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This image, posted to the Mutual UFO Network website, purportedly shows a UFO near the Eagle Ford Shale in July 2012.

Photo: YouTube Photo, Mutual UFO Network

This image, posted to the Mutual UFO Network website, purportedly...

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Stills from video from a deer cam, taken near Nixon, Texas on Dec. 29, 2012. Mutual UFO Network says the triangular lights might be signs of a UFO.

Photo: Copyright 2008

Stills from video from a deer cam, taken near Nixon, Texas on Dec....

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Stills from a deer cam, taken near Nixon, Texas Dec. 29, 2012. An unusual mist appears near ground level.

Photo: Copyright 2008

Stills from a deer cam, taken near Nixon, Texas Dec. 29, 2012. An...

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Stills from a deer cam, taken near Nixon, Texas on Dec. 29, 2012. Mutual UFO Network has raised suspicions about the bright orb seen in the sky near the location of the light triangle of the first photo.

Photo: Copyright 2008

Stills from a deer cam, taken near Nixon, Texas on Dec. 29, 2012....

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Lights hover above a La Salle County oil field drilling site in La Salle in this video screen shot. The unidentified lights and oject were captured on video by an oilfield worker at the site and aldo witnessed by 20 others.

In his blog post of March 28, Sweetman writes that he and two Aviation Week editors agree that the photos depict "something real." In other words, these pictures aren't easily explained away by reports of known military flights or the work of someone who got carried away with Photoshop.

So what can aviation experts say about the object in the photos?

"The photos tell us more about what the mysterious stranger isn't than what it is," Sweetman writes.

The size is hard to determine, Sweetman says, but its relationship to the contrails suggests it's bigger than the Northrup Grumman X-47B, which has a 62-foot wing span, according to Wikipedia.

Whatever it might be, the aircraft was accompanied by two others, and Douglass picked up some radio traffic suggesting the plane had a pilot, Sweetman's blog post states.

Although it's logical to expect that classified U.S. aircraft programs exist, due to the number that have been revealed in "all sorts of ways," it's uncommon for them to be exposed by civilian photos, Sweetman writes.

In 1956, when the Lockheed U-2 plane was making some of its first spy flights over the Soviet Union from an air base in England, British magazines started receiving "eyewitness accounts and grainy photos" from the public, he writes.

But the only other spy plane photographed before it was declassified was the RQ-170 Sentinel seen at Kandahar in 2007-09, Sweetman's blog states.